Typical electronic systems may comprise a variety of electronic components fabricated specifically for a particular function. Sometimes it is impossible for these various components to be fabricated on the same substrate due to material or processing differences or performance issues. It is therefore usually necessary to package the separate components and then connect them externally to function together as a system.
Usually components are connected using wire bonding or C4 flip chip packages. With microelectronics constantly scaling downward in size, the limits of direct scaling may soon be reached. Along with scaling of devices, there is an additional issue related to scaling the interconnects in order to accommodate such devices and their increasing densities.
Device speeds and therefore product performance is becoming limited by the interconnects between the various circuits involved in an overall product. For example, a CPU interfacing with memory or I/O circuits may become performance limited by the length and performance of the wires connecting them. The same issues also drive increased power requirements as well as heat dissipation limitations.
Traditional coaxial connections are described, e.g., in U.S. Pat. No. 6,410,431 to Bertin et al, in which an outer and annular cylinder and inner cylinder are filled with electrically conducting material, and the middle annular cylinder is filled with an electrically insulating material. The method of forming this structure involves sequential processing steps for each discrete portion of the coaxial structure.
FIG. 1 is a top-down view of prior art through-chip conductors 40C and 40D for low inductance chip-to-chip integration cited previously. Referring to conductor 40C, two concentric features 40A and 152 are formed separately using the following processes: lithography, etching, deposition, surface polish or planarization. Bertin's structure, as described in the aforementioned patent, is provided with an outer conductor that is electrically connected to the Si substrate in which it resides at the same potential as the aforementioned Si substrate. In the second embodiment, shown in conductor 40D, two individual features referenced as 40A are illustrated surrounded by feature 152.
In a conventional TSV, isolation from the signal to the substrate and/or adjacent structures is generally determined by the thickness and properties of the sidewall passivation. In the prior art, it is normally a thin oxide, preferably 1 μm or less. When it is manufactured by sub-atmospheric chemical vapor deposition (SACVD), also referred to as a high aspect ratio process (HARP), which in this case refers to an oxide deposition process typically CVD, it enables a non-thermal oxide to be deposited in a trench or via. However, the film quality may be rather poor. With a dielectric constant of about 5 to 7, as compared to approximately 4 for a good tetraethylorthosilicate (TEOS) film, SACVD is considered a good choice in view of it being conformal at low temperature (430° C.). In addition, a furnace oxidation cannot be used after the devices are built due to its high temperature, above 1000° C.
It is known that coaxial conductors work best in the aforementioned situations. An advantage of a coaxial structure over other types of transmission lines is that in an ideal coaxial conductor, the electromagnetic field carrying the signal exists only in the space between the inner and outer conductors. This allows coaxial conductor to be installed next to conductive materials without the power losses that occur in other transmission lines, and provides protection of the signal from external electromagnetic interference.
Accordingly, there is a need for a solution in the form of a coaxial TSV fabricated such that the center conductor provided with an outer shield, all of which are constructed using conventional CMOS processes.